Mass spectrometer



April 1951 c. E. BERRY 2,548,859

MASS SPECTROMETER Filed June 17, 1948 2 Sheets-Sheet l IN VEN TOR.CLIFFORD E. BERRY A T TORNE Y April 1951 c. E. BERRY 2,548,859

MASS SPECTROMETER Filed June 1'7, 1948 2 Sheets-Sheet 2 4A 5A 2A 3A 3A4A 2A 35 INVENTOR. CL IFFORD E. BERRY A TTORNEY Patented Apr. 17, 1951UNITED STATES PATENT OFFICE '2,548;859 MASS SPECTROMETER Clifiord E.Berry, Pasadena, Calif., assignor to Consolidated EngineeringCorporation, Pasadena, Calif., a corporation of California ApplicationJune 17, 1948, Serial No. 33,596

are introduced. In the ionization chamber the During passage through theanalyzer chamber the ions are subjected to a transverse electricj'ormagnetic field or both, to separate them accordin to their mass-tochargeratios into a plurality of diverging beams of ions. Each ion beam iscomposed of ions of the same specific mass and differing from the ionsin the other beams. The diverging beams are successively focused on anion collector'by varying the potential applied to the acceleratingelectrodes or by varying the intensity of the transverse field in theanalyzer tube. The current produced by the discharge of each beam on theion collector is a measure of the partial pressure of the molecules(from which the ions were derived) in the sample being analyzed. i

In accordance with the present invention, there is provided an ionsource which possesses a number of advantages both with respect toapplication and function over the conventional ion source. to facilitatean .understanding of the objectives of the invention. I .1.: The numberof separate parts required has been materially reduced.

2. The function of insulating and mounting the several parts isaccomplished by one member instead of a plurality of members.

3. The parts-are attached in definite and stable position by brazin themto their supporting members. i

4:. Closely adjacent surfaces which can hold contaminating material andthus slow down evacuation have been eliminated.

Some of these advantages are listed.

accomplished in accordance with the invention by the construction of anion source comprising an insulating plate having a plurality ofconductive wires or rods sealed therethrough. A series of metal partsare mounted over all or a part of the plurality of rods and are heldthereto and in appropriate relationship to each other by brazing to oneor more of the rods. The series of metal members form successively fromthe insulating disk a sample inlet, an ionization chamber, pusherelectrodes housed in the ionization chamber, a first ion slit, a secondion slit,

and a third ion slit. An electron emitting filament is mounted adjacentan outer wall of the ionization chamber. The filament emits an electronbeam which is directed through a slit in the wall and transverselyacross the ionization chamber. v

A feature of my invention is the combined function of the plurality ofconducting rods which serve (1) as supports to which the several partsare affiXed and (2) as electrical leads supplying appropriate potentialsto the various parts of the ion source. Additionally, the rods permitspacing of the various parts to (1) facilitate cleaning, (2) eliminateclosely adjacent difficultly evacuated surfaces, and (3) insulate thenecessary parts from each other.

The invention will be more clearly understood with reference to thefollowing detailed description taken in relation to the accompanyingdrawings wherein:

Fig. i is a. partial sectional view of a mass spectrometer showing therelationship of the ion source of the invention to the sample inletmeans and analyzer'tube;

Fig. 2 is-a section view ofthe ion source;

Fig. 3 is a horizontal section taken on the line 3-3'of Fig. 2;

Fig. 4 is a-vertical sectiontaken on the line 44 of Fig. 3; V i

--Fig. 5 is an exploded view of the ion source showing each of theelements thereof in perspective; and L Fig. 6 is a bottom perspectiveview of the laterally aligned element of Fig. 5.

Referring to the drawing and particularly to Fig. 1 thereof, the ionsource In is shown mounted within the'inlet end of a mass spectrometerI]. The mass spectrometer includes an analyzer tube [2 and an evacuatingtube "I4; Generally, the

evacuating tube M is connected to apparatus capable of producing a highdegree of vacuum such as a molecular pump, mercury diffusion pump or IThe foregoing "and. other improvements are the like. The evacuating tube[4 opens through 3 a wall of a tubular member I3 which surrounds the ionsource 10 and from which the analyzer tube l2 projects.

A tubular member H, projecting into tubular member I 3, is clampedbetween flange 24, attached to tube 13, and a flange l6, and serves tosupport the ion source inside tube l3. The ion source includes aplurality of conducting rods 2, 3, 4, 5 (see Fig. 5), shown in Fig. 1projecting downwardly from the ion source. In the mounting as shown, acircular metal disk 22 is brazed to the several rods 5, and is in turnbolted to the top of the tube l1.

The tube i3 is provided at-its lower endwith a flange 24 which restsagainst a flange 25 formed on the lower end of the tube 11. The tube I!in turn rests against the flange I6. The flange 25 on tube I? isprovided with electric inlet leads 26, 21 through which the several rodsl, 2, 3 and 4 of the ion source I may beconnected to a voltage supplycircuit to establish appropriate potentials at the various parts of theion source. The rods 5 which are connected through the metal plate 22 inconductive relationship to the tube H are at; the same potential as thetube 11.

The ion source lfl-includes a nipple 28 extending through the disk 22and the top of the tubular member H. The nipple 28 is connected to asample source (not shown) by means of a flexible sample inlet tube 30extending through the tubular member ll and the flange I6.

The construction of the ion source l9 can best be understood byreference to Figsp2, 3, 4, 5 and 6. Referring first to the explodedperspective View of Fig. 5-, the ion source'includesan insulating plate3d, a first disk 35 through which the inlet nipple 28 is afiixed, splitpusher electrodes 36, 31, a second'disk 38 having a recess 40. whichforms an ionization chamber withthe adjoining face of the disk 35 andhaving a first ion slit '42 in the top thereof, a third disk M defininga second ion slit and a fourth disk 45defininga third ion slit.

The plate sd isiconveniently, fabricatedof glass and preferably; glasshaving. a co-efficient of expansion approximating that of the conductiverodssealed therethrough. Preferably the rods are tungsten. Theconstruction of an insulating disk of this type with such rods sealedtherethrough is described indetail in my co-pending applicationSerial-No. 760,196, filed July 11, 1947, and entitled Metallic-GlassJoints. Y

As shown in Fig. 5 the plate 34 contains 15 straight tungsten wiresorrods of-varying lengths arranged in two concentriccircles; 6 in theinner circle and 9 in the outer. Some of: the wires project through theback surface of the disk a short distance so that appropriate electricalconnections can be made to them. Two spaces in the outer concentriccircle are unfilled, leaving a blank section of glass which is groundoff to form a flat face 34A. Ahole 48 is drilled in the middle ofthepla-te throughwhich the gas inlet tube 28 projects (see Fig. 4). Thevarious tungsten rods are denoted. by numerals from I to 5. Thesedesignations will be used to identify the rods when the mounting ofthevarious parts is described. I

. The disk 35is made from asolid piece of metal, generally circular inplan with the exception of a fiat face 35A. When the ion source isassembled, the face 35A coincides with the surface 34A of the insulatingplate 34. The disk 35is provided with a central hole-58 into-which theinlet nipple 28 Each of these holes is made larger than the rods so thatno connection exists when the disk 35 is placed on the plate 34. Theclearance between the rods and so called clearance holes in thesuccessive disks is clearly apparent in Figs. 2 and 4.

u The several clearance holes in the disks and pusher electrodes aredesignated by numerals corresponding to the numbers of the support rodswhich extend through these holes. Thus the number 2 rods project throughthe clearance is brazed. There are 15 holesdrilledin the block to'inatch'the' l5 rods projecting from the plate 34.

holes 2A in the disk 35.

Ferrules 553, El, 62, and 53 (Figs. 3 and 4) are brazed into the holes3A in the disk 35. When this disk is mounted on the plate 34 as shown inFigs. 2, 3 and l, the rods 3 project through the ferrules 68, BI, 62',and 63 and are brazed thereto to hold the disk and the plate together inspaced relationship.

In attaching ,themetaldisk 35 to the glassplate 34, a spacing of a fewthousandths of an inch is maintained between the. block and the disk bymeans of removable spacers. After completing; the assembly, the spacersare. removed. leaving. sufficient space so that the adjoining faces. ofthe block and the. disk may be readily cleaned. In the drawing theseveral members. are shown touching each other; itbeing impossible toillustrate a spacing in the order of magnitude of a few thousandths ofaninch. Additionally, although highly desirable, such spacing is notabsolutely essential to the. functioning. of theionsource.

As mentioned above, oneof the. objects of the invention is to provide anion. source. wherein closely adjacent surfaces'are eliminated so as toreduce-the consequent interference with evacuation. The termploselyadjacent surfaces, as applied relative to an: ion source. operating atreduced pressures, refers to metal surfaces which are actually touching.In. suchcase, because of microscopic unevenness in the. adjoining faces,evacuation is impeded. Thev spacing of a few thousandths of an inchprovided between the disk 35 and the plate 34 is considered. in. thisapplication to be a-large space inthat it. isof such mag.- nitude as notto interfere. with the evacuating process. p

The disk 35. is provided with two oppositely located peripheral notches.and 65 which form thin lips 64A, 65A, inthe. top of the disk. These lipsare usedas hereinafter described, for spot welding the disk 38.- to the:disk 35.

In my co-pending patent. application Serial No. 763,886, filed July.26,-. 19.47,. and entitled Welding, and relating to the fabrication ofionization chambers for mass. spectrometers, it was pointed out thatdimculties. are. encountered in brazingthe'various parts of. anionization chamber orion'source to-tungsten leads such as the .rodsextending, from: the plate 34. Since the brazing alloymeltsatabout100.0963. it isimpossible to heat the Whole assembly'including the glassplate' 3'4 to this brazingpointwithout damage. Further, a difficultynormally encountered in the brazing operation is splattering of themolten alloy; even microscopic splatters of the material on the glass.plate'or on otherparts of the ion source will cause subsequentdifficulties in operation.

In the last mentioned co-pending application I describedtheconstructionand use of. ferrules such as the ferrules 60, 61, 62 and63.whereby the foregoing .difficulties were eliminated .As theredescribed, the ferrule has a cup-shaped upper portion forming an annulusaround the rod in ment, completely avoids spattering of. the solder orother welding material after it becomes fused and provides an intenselocalizedaheat :for the fusing operation without necessitating applica-ztion of intense heat to the whole apparatus.

The recess 46 in disk 38 forms, with the adjoining face of disk 35,anionization chamber inwhich ionization of the sample 'molecules. takesplace. Disposed in the chamber and directly above the disk 35 arepusherelectrodes 36 and 31. members conveniently constructed by splitting adisk into two parts. Each electrode is provided with a hole 23 (Fig.alignable 'with the rods 2 projecting from the glass plate 34. FerrulesB6, and 61 are brazed in the holes 2B and the rods 2 projecting from theglass plate are brazed to'the ferrules to hold the electrodes in spacedand fixed relationship to the other parts.

Proceeding with the description of the apparatus in the order ofassembly, a'small rectangular gold member is brazed to the upper end ofwire I which projects through a clearance hole l-A in the disk 35. Thegold rectangle I0 forms an electron catcher as more fully describedhereinafter.

The second disk 38 contains Bclearance holes through which all of therods numbered 4 and 5 project without touching the disk. These severalclearance holes are designated either 4B or 53, to indicate which of therods 4-and 5 project therethrough and are in alignment with the holes 4Aand 5A in the disk 35. I

As hereinbefore described, a; recess 40 is formed in one faceof thesecond disk leaving a thinface 12 on the other side of the disk. .A slit42 is cut in the face 12 and serves as a first ion slit.

A fiat 38A is formed across one side of the disk in alignmentwiththeflat faces 35A and 34A of the members 35 and 34.respectively for thelike purpose of providing: space for an electron emitting filament 14(Fig. 2). A thin lip-15 is left above the fiat surface 38A'to act as ashield for thefilament 14. A slit '16 is cutin the fiat 38A' openinginto the chamber formed by the recess 40. A somewhat larger slit 18is'cut in the opposite side of the recess 40 giving access to a smallerrecess 19 in which the electron catcher "I0 is placed. Electronsgenerated by the filament pass as a beam through the slits 1B and 18 andimpinge on the electron collector 10. During traversal of the chamber40, the electrons ioni'ze the sample molecules therein.

The disk 38 is provided with oppositely spaced peripheral notches 80 andBI in alignmentlvvith the notches B4 and 65 in the disk 35. The notches80 and 8| form thin lips 80A and BIA in the lower edge of the disk 38.The first and second disks are joined by spot welding the lipsprovidedby the several notches (see Fig. 4). A space of a few thousandths of aninch is provided between the parts during assembly to allow cleaning ofthe surfaces and to eliminate closelyadjacent' sur-' faces for thereasons given above. Y I

These electrodes comprise two D-shaped The member comprises a split diskforming two D-shaped parts 44A and B. These form a second ion slit 440.Each of parts 44A and 44B is provided with holes 40 and 50 through whichthe rods 4 and 5 project. Ferrules 82, 83, 84 and 85 are brazed intoeach of the holes 40 in-the members 44A and 44B, and the appropriaterods are brazed thereto. v

The member 45 comprises a disk having are cess 86 in one face thereofleaving a thin opposite face 81. The face 81 is provided with a slit-88therein. The disk 45 is provided with holes 5D in which ferrules 90, 9|,92, and 93 are brazed.

(Figs. 2 and 4.)

As illustrated in the drawing, all of the clearance holes as well as allof the holes in the ferrules are oversize in order to reduce theprecision necessary in the location of the wires and. the fer-g Inassembling the ion source, all of the rules. parts are held in correctposition by an accurate fixture and are brazed together while so held.

Thus, in the final assembly the wires are not strained in any way andthere is no distortion in the ion source when removed from the fixture.

As shown in Figs. 2 and 4 the plate 34 is provided on both its upper andlower surfaces with strengthening bosses around each of the wires withthe exception hereinafter noted. There are no supporting bosses in theupper face of the plate around wires l and 2 (Fig. 2). poses of clarityin Fig. 5 all of the bosses are eliminated from the plate 34. Thereasonfor. eliminating the upper bosses around wires l and 2 is to reduce gasleakage from the ionization chamber throughthe holes IA, 2A and IB inthe disks 35 and 38. Thus, as above described, these clearance holes aremade larger than the wires for the double purpose of avoiding contact ofthe wires with the blocks 35 and 38 and also for the purpose of.facilitating assembly of the ion source. Gasle'akage through these holeswill be directly proportional to their size and inversely proportionalto their length. It follows that by elimination of the upper bosses fromthe disk 44 the length of the holes IA and 2A will be increased and gasleakage will be reduced. This is not a necessary feature of theinvention but is illustrated as a preferred embodiment thereof.

Although onespecific means of mounting the ion source of the inventionin amass spectrometer. is illustrated in detail in Fig. 1, it is to beunderstood that the ion source is designed for use in substantially anymass spectrometer. means of mounting the ion source within any giveninstrument will be determined by the design of the mass spectrometer.The present in vention is not intended to be limited tothe mounting ofthe ion source as shown in Fig. 1. v The feature of the invention whichinvolves the mounting of the several parts of the ion source todiifer'ent ones of a plurality of semirigid rods projecting from aninsulator plate 34 is not limited to the particular configuration of,

rods shown in the drawings. Thus, for convenience in manufacturing, theplurality of supports are arranged in two concentric circles as shown inFig. 5. However, any arrangement may be employed and the relativepositioning of the shorter and longer rods may be interchanged withoutinterfering with the functioning of the ion source. Any rearrangementwill, of course, necessitate relocation of. the clearance holesintheseveral members. In short, the illustrated 7'5 arrangement of the'ro'dswlth respect'toeach For purvs other iS nOtE essential i to the-:proper-wfunctionln or construction ofx'the iontsource;

Not; only have :I'provided :anion source which;

8? thirdsdislrxcn;;thelsidesopposite:the1 second disk a;

pluralltysofyconductive supports passing. throughthe-several":disks;.means:-afiixingthe first, third;

in the fixture the several parts are-brazed tothe appropriate wires. Bysuch a practice-the ion source: is constructed as aunit and may be--inserted or withdrawn from the mass spectrometer as aunit: Theadvantages of thistype of construction-and'method"of-fabricationwithrespect to: manufacture and" with respectto periodic cleaning of-the ion source, are manifest;

I cla-im:

1. Irran ion source for amass spectrometer-"thecombination whichcomprises afirst" conductive disk having an inlet thereinfor-moleculesto be ionized, a second conductive disk aflixed againstthe-first disk and-having recess therein opening toward the first diskand defining an ionization chamber, the second diskhaving an ion" slitin it opposite the first disk, a third conductive disk havinga-n ionslitin alignment with the ion slit in the=second diskand-spaced from thesecond disk on the side oppositethefirst disk, a plurality of conductivesupports passing throughthe several disks, and means afiixing-the firstdisk and thethirdj disk to separate ones of the saidsupp r 2; In an ionsourcejor a; mass spectrometer the combination whichcomprises-a firstconductive disk having an inlet thereinfor molecules to be ionized, asecond conductive disk, disposed against the first diskand affixedthereto, and, having a recess therein opening toward the first disk anddefining an ionizationchamber, the second disk havingan ion slit'in itopposite the first disk, a

pair; of pusher electrodes uspended in the ionization chamberindependent of, the first: and:

second disks; athird conductive disk having an ion-slit in alignmentwith the ion slitin the second diskand spaced from; the seconddisk onthe side opposite; the first disk, a fourthconductive disk havingan ionslit in alignment with the ion slit in,

the third" disk and spaced from the third'disk on the'side: opposite thesecond; disk, and'plurality of' conductive supports passing through theseveral disks-and means affixing the first, third and fourth disksandthe pusherelectrodes to separate-ones of said supports.

3. In an ion source-for a mass spectrometer-the combination whichcomprises a first conductive diskhavingan inlet": therein for themolecules tobe ionized; a second conductive disk disposed against andaffixed" to the first disk and having a recess therein openingtowardthefirst disk and defining an ionization chamber; the secondconductive disk having an ionslit in it oppositethe flrstdisk, a pair ofpusher electrodessuspended in the ionization chamber independent of thefirst and-second disks, a third conductive disk having anion slit'inalignment'with the ionslit in the second disk and spacedfrom theseconddisk on the side' opposite thefirst disk, a fourth conduc-i tivediskhaving an ionslitzinalignmentwith the ion slit-in: the third diskand spaced, from the and: fourth disks and the pair; of. pusher;velec--' trodes: to: separate. ones oi; said supports, and meansrorea-nchoringthe plurality 01 supports in;

fixed relationship. toeach other.

4.: Apparatus accordin to claim 3 wherein the meansrforanchoring the.several: supports com prisesga glass plate through which .theconductive,supportsaresealed;

5. In-ian-aion source; for :a. mass spectrometer.

the. oombin ationwhichcomprises a first conduct tive=diskahaving.v aninlet therein for molecules, to

be ionized; a. second: conductive disk. disposed againsta-ndamxed, to;the first'disk, agfirst recess in the-second diskopening toward thefirst disk:

and defining an ionization chamber, a. second recessin the second 1 diskopening tOWflldithB. first;

disk; a fiIStTSlit. in the second disk. communicat ingbetween thefirstzrecess and the second recess, a: second-1 slit in the; second diskcommunicatingbetween the first recess and the exterior of thediskopposite the-firsttslit, third slit communicating with the first-recessopposite the firsttdisk,

a. third conductive disk having an ion slit in,

alignment with the third-slit inthesecond disk andrspacedfrom the seconddisk on-theside op posite the first disk, aplurality of conductivesupeports; passing through the several disks, means afiixing the first andthird disks to separate ones of saidsupports, one'of said supportsextending into the second. recess. inzthe. second disk, an elec troncatchergmounted on. said one of said supports and amelectromemittingelement disposed adjacent said second disk in alignment with said secondslit therein.

6:. Inan. ion source for: a mass spectrometer,.

the improvement which comprises a sintered' glass disk; a plurality'ofconductive rods sealedthrough V the idisk,,the ionization chamber,pusher-v electrodes; and; accelerating, electrodes being mountedtop-separate onesofsaid pluralityof 'roclsv in spacedrelationship.toeachother.

8., In. anion source-, for -a mass, spectrometer having severalcomponent parts. including means, forionizing molecules-and means fordischarging,

ions ,fltomkthen ion. source, the improvement which comprises a,plurality of conductive members sealed through an insulating memberandispaced from each other, the several component partsof the ion sourcebeing mounted to. difierentones of said conductive members in spacedrelation- Ship;

9. In an ion sourceforamass spectrometer, the combination whichcomprises a plurality-oi conductive: rods sealed through. an insulatingmember; and: means mountedto separate-ones of the plurality of rods toform an ionization necessitate; relocation of the clearance holes inthe; several? members. In short, the illustrated :5 arrangement off theirodswith: respect to each each other and from the means forming theionization chamber.

CLIFFORD E. BERRY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,071,597 Viasselli Feb. 23, 19372,084,858 Metcalf June 22, 1937 10 Number Name Date 2,437,130 Scott eta1 Mar. 2 1948 2,444,968 Washburn July 13, 1948 OTHER REFERENCESCoggeshall et a1.: Review of Scientific Instruments, May 1943, vol. 14,pages 125-129.

Honig: Journal of Applied Physics, November 1945, vol. 16, pages646-654.

Nier: Review of Scientific Instruments, June 1947, vol. 18, pages 398and 399.

